1. Field of the Invention
The present invention relates to an elastic wave device in which an elastic wave element is mounted on a package substrate with a bump electrode located therebetween and a method for manufacturing the elastic wave device.
2. Description of the Related Art
As one of the techniques for reducing the size of elastic wave devices used in cellular phones and the like, a method of mounting an elastic wave element onto a package substrate using a bump electrode is known.
Japanese Unexamined Patent Application Publication No. 2005-197595 discloses a technique in which a bump electrode is joined to a pad electrode of an elastic wave element. An Al joining layer with a thickness of 840 nm is disposed as an outermost surface layer of the pad electrode, and the Al joining layer is joined to the bump electrode composed of Au. The Al joining layer and the bump electrode are joined together by fusion bonding, and an Au—Al alloy layer is formed at the joining portion between the bump electrode and the Al joining layer.
In the elastic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2005-197595, in some cases, Kirkendall voids may occur in the Au—Al alloy layer when subjected to thermal shock during mounting of the elastic wave element onto a package substrate or during reflow. This may lead to a decrease in the joining strength between the pad electrode and the bump electrode. Consequently, the joining strength between the elastic wave element and the bump electrode may decrease.